DR YORGOS NIKAS / SCIENCE PHOTO LIBRARY DR YORGOS NIKAS / SCIENCE PHOTO LIBRARY
Human egg. Coloured scanning electron micrograph (SEM) of a human egg surrounded by cumulus corona cells. At lower frame (green) is the rounded egg or oocyte which has a spongy surface layer. This layer, known as the zona pellucida, serves to protect the egg and to attract sperm for fertilisation. At upper frame (pink) are cumulus corona cells which serve to support and nourish the developing egg in the ovary, forming a "corona radiata" (radiating crown) around the egg. When the egg is released from the ovary, as here, some corona radiata cells remain attached to the egg but fall away after fertilisation. Magnification: x1,360 at 5x7cm size.
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